There is a great diversity of commercially available silver halide photographic materials and image formation methods using these silver halide photographic materials. These silver halide photographic materials and image formation methods have been used in various fields. The halogen composition of the silver halide emulsion incorporated in these light-sensitive materials, particularly if they are for picture taking, is preferably silver bromoiodide mainly comprising silver bromide for the purpose of attaining high sensitivity.
On the other hand, products for use in a market requiring the completion of a large number of prints in a short delivery period, such as light-sensitive material for color photographic use, comprise silver bromide or silver bromochloride substantially free of silver iodide in view of the necessity for expedited development.
In recent years, the demand for improvement in the capability of color photographic papers to undergo rapid processing has grown more and more. It is known that the rise in the silver chloride content of the silver halide emulsion to be used brings about a great rise in development speed. Silver chloride emulsions are known to be disadvantageous in that they generally exhibit a low sensitivity. In order to overcome this difficulty, various techniques have been disclosed for increasing the sensitivity of a silver halide emulsion having a high silver chloride content.
It is also known that such a silver halide emulsion having a high silver chloride content can hardly provide a high sensitivity and a high gradation in an ordinary chemical sensitization process. Additionally, it exhibits a great reciprocity law failure, i.e., a great sensitivity and gradation change due to a change in exposure illuminance. Various techniques have been disclosed to overcome these difficulties.
Selenium sensitization and gold sensitization are known as techniques for increasing the sensitivity of a silver halide emulsion. When the inventors applied selenium sensitization or gold sensitization to a silver halide emulsion having a high silver chloride content, they confirmed its sensitizing effect.
Light-sensitive materials for color photographic paper are required to exhibit little change in their photographic properties even after prolonged storage thereof. However, it was found that light-sensitive materials comprising a selenium-sensitized or gold-sensitized high silver chloride content emulsion which can undergo rapid processing tend to show disadvantageously a rise in fog density after prolonged storage thereof.
Further, color photographic papers preferably exhibit no change in photographic properties due to the humidity fluctuations upon printing in photofinishing laboratories. This is very important for the maintenance of constant quality. Light-sensitive materials comprising a selenium-sensitized high silver chloride content emulsion need to undergo moderate selenium sensitization to reduce the rise in fog density due to prolonged storage thereof. However, it was found that if such a silver chloride content emulsion undergoes moderate selenium sensitization, it disadvantageously exhibits a great sensitivity change due to the humidity fluctuations upon exposure. It was further found that this is also the case with gold sensitization.
JP-A-58-95736, JP-A-58-108533, JP-A-60-222844, JP-A-60-222845 and JP-A-64-26837 disclose that a high sensitivity and a high gradation can be accomplished with a high silver chloride content emulsion having differently structured silver bromide-filled regions. These techniques surely can provide a high sensitivity emulsion, but have only a small effect in correcting reciprocity law failure.
It is known that the reciprocity law failure of a silver halide emulsion can be effectively corrected by doping silver halide grains with iridium. For example, JP-B-43-4935 (the term "JP-B" as used herein means an "examined Japanese patent publication") discloses that light-sensitive materials comprising a silver halide emulsion containing a slight amount of an iridium compound which has been added during precipitation or ripening thereof can provide an image having an almost constant gradation over a wide range of exposure times. However, it is disclosed in Journal of Photographic Science, vol. 33, page 201 (1985), that a high silver chloride content emulsion doped with iridium shows latent image intensification between 15 seconds and about 2 hours after exposure. This phenomenon causes fluctuations in sensitivity and gradation due to the change in the time required between exposure and processing. Thus, this system is not practical.
JP-A-1-105940 discloses that a high silver chloride content emulsion selectively doped with iridium having silver bromide-filled regions can provide an emulsion having excellent reciprocity law adherence without impairing the latent image stability for several hours after exposure. However, the present inventors found that this technique can cause latent image sensitization under some reaction conditions for the formation of silver bromide-filled regions and that further improvements are needed to satisfy sufficiently latent image stability and reciprocity law at the same time. Furthermore, a high silver chloride content emulsion having a high silver bromide content localized phase was found to be disadvantageous in that it exhibits a great sensitivity change due to the fluctuations of humidity upon exposure and the fluctuations of the time interval between exposure and processing and also exhibits a great sensitivity change after prolonged storage of the light-sensitive material.
For example, light-sensitive materials for color photographic paper are required to exhibit little change in photographic properties even after prolonged storage thereof. It is also desired that these light-sensitive materials should have no change in the photographic properties against the fluctuations of humidity or the fluctuations of time interval between exposure and processing when subjected to printing in laboratories. These requirements are important in offering invariable quality color prints to users. Therefore, there has been a need to overcome the above mentioned disadvantages of high silver chloride content emulsions having a high silver bromide content localized phase.
The inventors found that these problems can be solved by incorporating a certain reducer in such a high silver chloride content emulsion. Thus, the present invention was worked out. On the other hand, JP-A-2-6943 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses that the preservability and latent image stability of a silver halide photographic material comprising a high silver chloride content emulsion can be improved by incorporating a reducing compound in the silver halide photographic material.
However, the above cited patent application does not disclose that the sensitivity change due to the fluctuations of humidity upon exposure can be remarkably inhibited when such a high silver chloride content emulsion is used in combination with a substantially silver iodide-free silver bromochloride emulsion having a localized phase with a silver bromide content of 10% or more in the vicinity of the surface of silver halide grains and having a silver chloride content of 95 mol % or more as in the present invention. The above cited patent application also does not disclose that this effect becomes remarkable particularly when this system is combined with a silver bromochloride emulsion containing an iridium compound.